1. Field of the Invention
The present invention relates to a color cathode-ray tube (hereinafter referred to as "CRT"). More particularly, it relates to a design compensation volume setup of a corner spring for supporting a mask structure within a panel.
2. Discussion of Related Art
As shown in FIG. 1, a conventional CRT includes a panel 2 mounted in front thereof; a funnel 7 mounted at the back of the panel 2 in order to maintain a vacuum; a neck 10 extending from the back of the funnel 7; an electron gun 8 within the neck 10, for emitting R, G, and B electron beams; a phosphor screen 3 applied to the inner surface of the panel 2, including phosphor layer for producing red, green, and blue lights in accordance with landing of electron beams; and a shadow mask structure 6 consisting of a rectangular shadow mask 4 where a plurality of electron beam apertures (not shown) are formed for color selection, and a frame 5 for fixing the shadow mask 4.
The frame 5 is supported by a corner spring 11 connected to a stud pin 12 toward the panel 2. As shown in FIG. 2, the corner spring 11 disclosed in U.S. Pat. No. 4,827,180 is constructed of a first arm 27 having a stud pin hole, and a second arm 29 connected to the frame 5, the first and second arms being welded to each other. The two, respective arms make a specific angle (.theta..sub.1,.theta..sub.2) with a central axis 1 of welding portion.
Reference numeral 9 is indicative of a deflection yoke for deflecting the electron beams.
In the conventional CRT, the electron beams emitted from the electron gun 8 are deflected by the deflection yoke 9, before passing through the apertures of the shadow mask 4 and scanning the phosphor screen, to thereby display an image.
The internal parts are located like a dotted line of FIG. 3 prior to operation of the CRT, but move like a solid line when the temperature rises due to heat expansion.
The mask apertures formed on the shadow mask 4 move toward P' from P, and the corner spring 11 serves to allow the mask apertures to move to a phosphorescent screen, heading for the position of Q.
That is, in this case, the V-shaped corner spring 11 is pressed to make the first and second arms 27 and 29 closer to each other. The second arm 29 is welded to the frame 5, and .theta..sub.1 and .theta..sub.2 of FIG. 2 is differently changed, in such a way that the position of the corner spring 11 is varied outside.
The color CRT has been developed in recent years, having the shadow mask made of the material of low coefficient of expansion such as Invar alloy, namely 36% nickel-iron alloy with coefficient of expansion of about 1.2.times.10.sup.-6 /.degree. C., and the mask frame made of iron.
The shadow mask made of Invar alloy with very low coefficient of expansion, does not expand with heat, and the mask frame expands around with heat during operation of the CRT.
The typical corner spring for compensating the mislanding by angle (.theta..sub.1,.theta..sub.2) of spring results in inaccurate electron beam landing. The reason why the electron beams land inaccurately is as follows.
When the temperature rises in the CRT the shadow mask does not efficiently expand with heat. The mask frame is made of iron with coefficient of expansion (about 1.2.times.10.sup.-5 /.degree. C. at room temperature) about ten times as high as 36% nickel-iron alloy. In this connection, the mask frame expands with heat.
Consequently, the corner spring allows the shadow mask move toward the screen. A passage that the electron beams pass through the mask apertures is altered, which causes the electron beams to inaccurately land on the phosphor element, thereby resulting in degradation of color purity.